Criteria for loans to be considered as nonperforming.

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Financing Receivable, Credit Loss, Expense (Reversal), Additional Provisions

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Financing Receivable, Credit Loss, Expense (Reversal), Deteriorating Economic Conditions

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Financing Receivable, Credit Loss, Expense (Reversal), Other Adjustments

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Financing Receivable, Credit Loss, Expense (Reversal), Reduction

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Loans And Leases Receivable, Percentage Of Loans In Full And Interest Repayment Status That Are Subject To Interest Rate Reductions

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Loans And Leases Receivable, Period Of Interest Rate Reduction, Financial Difficulty Status

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Loans And Leases Receivable, Temporary Interest Rate Reduction, Financial Difficulty Status

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Loans and Leases Receivable, Impaired, Loans Granted Forbearance Qualified as Trouble Debt Restructuring

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Payment Default Period For Troubled Debt Restructurings

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Period of Loans Past Due That Have Accrued Interest

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[Line Items] for Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Table]

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Tier One of Government Guarantee

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Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

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This is the result of the principal amount outstanding of total loans managed or securitized less securitized loans and loans that are in the process of being securitized.

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The cash inflow associated with the sale of loans receivables arising from the financing of goods and services.

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Amount of expense related to estimated loss from loan and lease transactions.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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Amount, after valuation allowance, of accounts receivable held for sale and not part of disposal group.

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Allowance for Credit Losses - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Jul. 01, 2006
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Line Items]
Provision for credit losses	$ 121,000	$ 93,133
Additional provisions		290,000
Additional provisions related to economic deterioration		129,000
Additional provisions related to other adjustments		99,000
Reduction to provision for credit losses	162,000	206,000
Loans transferred to held-for-sale from held for investment		2,900,000
Proceeds from sale of loans receivable	3,100,000
Total provision		219,480	$ (353,934)	$ (244,584)
Loan transfer to held-for-sale		$ 2,885,640	$ 0
Interest rate offered to borrowers facing financial difficulty		4.00%
Interest rate offered to borrowers facing financial difficulty, period		2 years
Percentage of loans in full and interest repayment status that are subject to interest rate reductions		7.80%	7.20%
Percentage of loans granted forbearance (as a percentage)		47.00%	50.00%
Criteria for loans to be considered as nonperforming		90 days
Tier 1 of government guarantee (at least)						97.00%
TDR payment default period		60 days
Period of loans past due that have accrued interest		90 days
Discontinued Operations, Disposed of by Sale
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Line Items]
Split Loans portfolio sales price	$ 43,000				$ 43,000
FFELP Loans
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Line Items]
Tier 1 of government guarantee (at least)		97.00%
Private Education Loans
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Line Items]
Total provision		$ 218,789	$ (279,570)	$ (169,287)
Maximum
Schedule Of Allowance For Credit Losses And Recorded Investment In Financing Receivables Table [Line Items]
Interest rate offered to borrowers facing financial difficulty		4.00%